In recent years, there have been even greater demands for increased miniaturization and increased performance in electronic instruments. Among these, in order to deal with increasing signal speeds, investigations have been made into increasing the speed of signal transmission paths inside an electronic instrument by connecting together electronic components by means of optical signals. In connections which are made using optical signals, a mixed optical-electrical substrate is used on which are provided both optical wiring and electrical wiring, and the optical wiring has an optical waveguide that is formed by a core portion and a cladding portion, and an optical signal is transmitted as a result of light being propagated along the core portion of the optical waveguide.
In an electronic instrument which is provided with this type of optical-electrical substrate, an effective structure is one in which electronic components are mounted on the substrate, and input signals of these electronic components are converted into optical signals using an optical element, and are then propagated over an optical waveguide. At the destination of these optical signals, they are restored to the form of electrical output signals using another optical element, and are connected to another electronic component.
Conventionally, advances have been made towards integration with rigid substrates such as optical waveguides being formed in a rigid substrate. For example, an optical element and an electronic component are mounted on the substrate. Electrical signals are propagated from the surface of the substrate on which the optical element and electronic component are mounted, to the surface on the opposite side on which electrical wiring is formed, via electrical wiring that goes through the substrate and connects between these surfaces. Optical signals are propagated by means of an optical waveguide that is formed in the substrate, and pass from the optical waveguide through a non-conductive layer and are transmitted to a light receiving or emitting portion of an optical element (see, for example, Patent document 1).
However, in a structure such as this, there are limits on the degree of miniaturization, for example, limits of thinning. Moreover, due to a distance between the light receiving or emitting portion of the optical element and the core portion of the optical waveguide, this has an effect on the efficiency of the optical input from the light-emitting portion to the core portion, and problems arise in characteristics such as optical propagation loss and the like. Furthermore, increased positioning accuracy between the light receiving or emitting portion of an optical element and the core portion of the optical waveguide is required to solve problems such as these.    Patent document 1: Japanese Unexamined Patent Application, First Application No. 2002-182049